Adjusting the Inner Workings Of Video Compression

Everybody's doing it. People are constantly expecting to see more. We're talking about video and other forms of media being distributed over the Web. Dennis Chominsky looks at some of the techniques for getting the best results with your next video-compression project.

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Today, because there are so many people
using video in such a variety of different fashions, from amateurs to
professionals, we need to discuss how to improve the look of digital media
content. I wanted to take this opportunity to step inside the way professionals
handle video compression and what aspects they use to "tweak" the
media to gain optimal results.

Choosing the right format and applying the most appropriate codec are the
keys to getting the best video clip for the distribution channels of your
choice. Many of the default templates are good; some extremely good. But the
biggest problem is that they are preset for good quality source content. What
happens if your original source materials are not up-to-speed? Is it too late?
The simple answer is no. You do not have to live with poor quality video just
because it is being compressed for CD-ROM or the Internet.

What Size Do You Need?

The first thing that you want to make sure you have full control over is the
physical display size of your image. Do you want it 400x300 pixels?
320x240pixels? Most standard video is in a four-by-three (4:3) ratio aspect, so
whatever measurement specifications you are using, there are four units across
for every three units high. Therefore, if you used increments of 20, you would
want your video size to be 80x60, 160x120, and so on. What if you were
developing a Web page that required a specific size for your video? Many
professional software applications allow you to customize the exact size of your
image. You can choose whether to constrain your proportions to a 4:3 aspect
ratio or literally customize it to any size you want. Keep in mind, however,
that if you change the perspective too much, your image may start to take on
undesirable appearances. Depending on which way you alter the ratio, if you had
people in the shot, they may start to appear exaggerated. They might be too
tall, thin, and stretched out; or the opposite, short, fat, and squashed.

While setting the exact image size of your file, you may also want to
consider cropping your image. Most programs allow you to crop in one of two
ways, if not offering both controls. One way is to actually drag the corner
points of a bounding box. This allows you to quickly and easily define the area
you want to display once you process your image. The other option is to manually
enter numeric values for each side: left, right, top, and bottom. Keep in mind,
cropping your image may alter the original aspect ratio of your file. If I can
offer a professional tip, always crop your image by about 5 to 10 pixels around
all sides. This helps avoid any of the scan lines and sync pulses found when you
create digital media files from normal videotaped content. Televisions and video
monitors typically work in normal-scan or over-scan mode. This means they are
typically masking some of the outer edges of the video signal. If you actually
see a professional video monitor, you'll notice a switch to change the
image into under-scan mode. This shrinks down the image a small percentage,
allowing you to view the image full frame, corner to corner. When video is
brought into the computer as digital media, the image is displayed from corner
to corner. There is no masking of the edges (where some scan lines typically
appear). Setting a small crop around the edges is now part of my default
settings that I apply to every media file I create. Everyone has his or her own
techniques.